Silent period method and apparatus for dynamic spectrum management

ABSTRACT

Described herein is a silent period method and apparatus for dynamic spectrum management. The methods include configuration and coordination of silent periods across an aggregated channel in a wireless communication system. A silent period management entity (SPME) dynamically determines silent period schedules for channels based on system and device information and assigns a silent period duration and periodicity for each silent period. The SPME may reconfigure the silent period schedule based on system delay, system throughput, channel quality or channel management events. A silent period interpretation entity (SPIE) receives and implements the silent period schedule. The silent periods for the channels may be synchronized, independent, or set-synchronized. Interfaces for communicating between the SPME, SPIE, a channel management function, a medium access control (MAC) quality of service (QoS) entity, a sensing/capabilities database, a MAC layer management entity (MLME) and a wireless receive/transmit unit (WTRU) MLME are described herein.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/287,381, filed Nov. 2, 2011, and issued as U.S. Pat. No. 9,839,045 onDec. 5, 2017, which claims the benefit of U.S. provisional applicationNo.61/410,528, filed Nov. 5, 2010, the contents of which are herebyincorporated by reference herein.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

Local Wireless Network systems such as Institute of Electrical andElectronics Engineers (IEEE) 802.11 may operate in a predefinedspectrum, such as, for example, a contiguous spectrum channel. Inaddition, the spectrum allowed for cellular licensed devices and devicesoperating in unlicensed bands such as industrial, scientific and medical(ISM), may not change over time.

In the United States, 408 MHz of spectrum from 54 MHz to 806 MHz may beallocated for television (TV). A portion of that spectrum may beredeveloped for commercial operations through auctions and for publicsafety applications. The remaining portion of the spectrum may remaindedicated for over-the-air TV operations. However, throughout the UnitedStates, portions of that spectrum resource may remain unused. The amountand exact frequency of unused spectrum may vary from location tolocation. These unused portions of spectrum may be referred to as TVWhite Space (TVWS). Because there are fewer TV stations located outsidetop metropolitan areas, most of the unoccupied TVWS spectrum isavailable in low population density or rural areas that tend to beunderserved with other broadband options such as Digital Subscriber Line(DSL) or cable.

Each available TV channel may provide 6 MHz of spectrum capacity thatmay be used for broadband connectivity. TVWS may have large coverageareas due to long range propagation of signals at these frequencies. Forexample, a wireless local area network (WLAN) access point (AP) locationoperating in TVWS may provide coverage for an area of a few squaremiles. In contrast, wireless equipment such as IEEE 802.11b/gin may havean average coverage area of 150 square feet.

Aggregating multiple channels and using a primary channel was introducedin IEEE 802.11n and 802.11ac. 802.11n and 802.11ac to deal withcontinuous channels. When operating in TVWS, multiple continuouschannels may not be available, and aggregation on non-continuouschannels may be required. The concept of silent measurement periods wasintroduced in IEEE 802.11 for detection of radar in the 5 GHz bands. Asilent period may be used in physical layer/medium access control layer(PHY/MAC) devices operating in TVWS. In both cases, these were based onsensing silent period information on the beacon. However, they do notaddress sensing silent period information over aggregated channels.

The sse of silent periods may lead to a loss of throughput and anincrease of delay/jitter. When a set of stations are silenced formeasurements, the outgoing traffic may be buffered during the silentperiod, resulting in an increase of buffer space requirements. Inaddition, the loss of throughput and introduction of delay/jitter couldadversely affect certain applications which are being run on thenetwork.

SUMMARY

Described herein is a silent period method and apparatus for dynamicspectrum management. The methods include configuration and coordinationof silent periods across an aggregated channel in a wirelesscommunication system. A silent period management entity (SPME)dynamically determines silent period schedules for channels based onsystem and device information and assigns a silent period duration andperiodicity corresponding for each silent period. The SPME mayreconfigure the silent period schedule based on at least one of systemdelay, system throughput, channel quality or channel management events.A silent period interpretation entity (SPIE) receives and implements thesilent period schedule. The silent periods for the channels may besynchronized, independent, or set-synchronized. Interfaces forcommunicating between the SPME, SPIE, a channel management function, amedium access control (MAC) quality of service (QoS) entity, asensing/capabilities database, a MAC layer management entity (MLME) anda wireless receive/transmit unit (WTRU) MLME are described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A;

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A;

FIG. 2 is a diagram of an example four-channel silent period schedule;

FIG. 3 is a diagram of another example four-channel silent periodschedule;

FIG. 4 is a diagram of example silent period configurations;

FIGS. 5A and 5B are diagrams of two example silent periodconfigurations;

FIG. 6 is a block diagram of an example silent period managementarchitecture;

FIGS. 7A and 7B are flow diagrams of an example system initializationand silent period initiation method;

FIG. 8 is a flow diagram of an example channel reconfiguration method;

FIGS. 9A and 9B are flow diagrams of an example asynchronous silentperiod configuration method;

FIG. 10 is a flow diagram of an example quality of service (QoS)requirements change method;

FIG. 11 is a flow diagram of an example method for using messages at aDSM client or a station;

FIG. 12 is a diagram of example default silent period lengths andperiodicities;

FIG. 13 is a diagram of an example silent period configuration;

FIG. 14 is a diagram of another example silent period configuration;

FIG. 15 is a diagram of another example silent period configuration;

FIG. 16 is a diagram of another example silent period configuration;

FIG. 17 is a flow diagram for an example probing approach for primaryuser (PU) detection;

FIG. 18 is a flow diagram for an example probing approach for secondaryuser (SU) detection;

FIG. 19 is a diagram of an example message format;

FIGS. 20A, 20B and 20C are examples of silent period intervals relativeto beacon intervals;

FIG. 21 is a diagram of an example placement of silent periods withtraffic indication map (TIM) and delivery traffic indication message(DTIM) times;

FIG. 22 is a diagram of an example station transmission pattern;

FIG. 23 is a diagram of an example channel independent silent period;

FIG. 24 is a diagram of another example channel independent silentperiod; and

FIG. 25 is an example call flow for asynchronous silent period.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Described herein are example communication systems that may beapplicable and may be used with the description herein below. Othercommunication systems may also be used.

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, 102 d, a radioaccess network (RAN) 104, a core network 106, a public switchedtelephone network (PSTN) 108, the Internet 110, and other networks 112,though it will be appreciated that the disclosed embodiments contemplateany number of WTRUs, base stations, networks, and/or network elements.Each of the WTRUs 102 a, 102 b, 102 c, 102 d may be any type of deviceconfigured to operate and/or communicate in a wireless environment. Byway of example, the WTRUs 102 a, 102 b, 102 c, 102 d may be configuredto transmit and/or receive wireless signals and may include userequipment (UE), a mobile station, a fixed or mobile subscriber unit, apager, a cellular telephone, a personal digital assistant (PDA), asmartphone, a laptop, a netbook, a personal computer, a wireless sensor,consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106, the Internet 110,and/or the networks 112. By way of example, the base stations 114 a, 114b may be a base transceiver station (BTS), a Node-B, an eNode B, a HomeNode B, a Home eNode B, a site controller, an access point (AP), awireless router, and the like. While the base stations 114 a, 114 b areeach depicted as a single element, it will be appreciated that the basestations 114 a, 114 b may include any number of interconnected basestations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 114 a and/or the base station 114 b may beconfigured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 114 a may be divided intothree sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, etc.). Theair interface 116 may be established using any suitable radio accesstechnology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed DownlinkPacket Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (i.e.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1×, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A,the base station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106.

The RAN 104 may be in communication with the core network 106, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (VoIP) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. For example, the core network 106may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it will be appreciatedthat the RAN 104 and/or the core network 106 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 104 or a different RAT. For example, in addition to being connectedto the RAN 104, which may be utilizing an E-UTRA radio technology, thecore network 106 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102 a,102 b, 102 c, 102 d to access the PSTN 108, the Internet 110, and/orother networks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 112 may include wired or wireless communications networks ownedand/or operated by other service providers. For example, the networks112 may include another core network connected to one or more RANs,which may employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 130, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive RF signals. In another embodiment, the transmit/receiveelement 122 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 122 may be configured totransmit and receive both RF and light signals. It will be appreciatedthat the transmit/receive element 122 may be configured to transmitand/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station (e.g., base stations 114 a, 114 b) and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It will be appreciated that the WTRU 102 mayacquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C is a system diagram of the RAN 104 and the core network 106according to an embodiment. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102c over the air interface 116. The RAN 104 may also be in communicationwith the core network 106.

The RAN 104 may include eNode-Bs 140 a, 140 b, 140 c, though it will beappreciated that the RAN 104 may include any number of eNode-Bs whileremaining consistent with an embodiment. The eNode-Bs 140 a, 140 b, 140c may each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the eNode-Bs 140 a, 140 b, 140 c may implement MIMO technology. Thus,the eNode-B 140 a, for example, may use multiple antennas to transmitwireless signals to, and receive wireless signals from, the WTRU 102 a.

Each of the eNode-Bs 140 a, 140 b, 140 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the uplink and/or downlink, and the like. As shown in FIG. 1C, theeNode-Bs 140 a, 140 b, 140 c may communicate with one another over an X2interface.

The core network 106 shown in FIG. 1C may include a mobility managementgateway (MME) 142, a serving gateway 144, and a packet data network(PDN) gateway 146. While each of the foregoing elements are depicted aspart of the core network 106, it will be appreciated that any one ofthese elements may be owned and/or operated by an entity other than thecore network operator.

The MME 142 may be connected to each of the eNode-Bs 142 a, 142 b, 142 cin the RAN 104 via an S1 interface and may serve as a control node. Forexample, the MME 142 may be responsible for authenticating users of theWTRUs 102 a, 102 b, 102 c, bearer activation/deactivation, selecting aparticular serving gateway during an initial attach of the WTRUs 102 a,102 b, 102 c, and the like. The MME 142 may also provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as GSM or WCDMA.

The serving gateway 144 may be connected to each of the eNode Bs 140 a,140 b, 140 c in the RAN 104 via the S1 interface. The serving gateway144 may generally route and forward user data packets to/from the WTRUs102 a, 102 b, 102 c. The serving gateway 144 may also perform otherfunctions, such as anchoring user planes during inter-eNode B handovers,triggering paging when downlink data is available for the WTRUs 102 a,102 b, 102 c, managing and storing contexts of the WTRUs 102 a, 102 b,102 c, and the like.

The serving gateway 144 may also be connected to the PDN gateway 146,which may provide the WTRUs 102 a, 102 b, 102 c with access topacket-switched networks, such as the Internet 110, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and IP-enableddevices. An access router (AR) 150 of a wireless local area network(WLAN) 155 may be in communication with the Internet 110. The AR 150 mayfacilitate communications between APs 160 a, 160 b, and 160 c. The APs160 a, 160 b, and 160 c may be in communication with STAs 170 a, 170 b,and 170 c.

The core network 106 may facilitate communications with other networks.For example, the core network 106 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices. For example, the corenetwork 106 may include, or may communicate with, an IP gateway (e.g.,an IP multimedia subsystem (IMS) server) that serves as an interfacebetween the core network 106 and the PSTN 108. In addition, the corenetwork 106 may provide the WTRUs 102 a, 102 b, 102 c with access to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

The description herein may use the following terms and may have thefollowing definitions in addition to or that may supplement those usedin the art. A DSM system may refer to the system comprising one (ormore) DSM engines controlling and assisting various local networks anddirect links. A DSM client may refer to a device that has acommunication link to the DSM engine and may be part of a local networkor a direct link. A DSM engine may be an entity responsible for spectrummanagement as well as coordination and management of local networks anddirect links. A DSM link may refer to a communication link between DSMengine and DSM client, providing control plane and user planefunctionality. A direct link may refer to a link between two dynamicspectrum management (DSM) clients. Operating channel(s) may bechannel(s) chosen for the DSM communication links. An attachment mayrefer to the process by which a DSM client discovers the DSM operatingchannel, synchronizes to this channel, associates with the AP andinforms the DSM engine of its presence and its capabilities. DiscoveryProcess may refer to a process by which a DSM client finds the operatingchannel of the DSM engine, (scans to find the control channel andsynchronizes to the DSM).

The descriptions herein may refer to television white space (TVWS) as anexample of an opportunistic bandwidth or opportunistic frequency band.The same description may apply for operation in any opportunisticfrequency bands where devices may operate opportunistically when certaindefined priority users (primary users) are not operating. In addition, adatabase of priority users or primary users for an opportunistic bandmay be maintained in a database. For operation in TVWS, this databasemay be referred to as the TVWS database. However, operation with asimilar database may be possible in any opportunistic band. Othernon-limiting examples of opportunistic bands, opportunistic bandwidth oropportunistic frequency band may include unlicensed bands, leased bandsor sublicensed bands.

An enabling station may refer to a station that has the authority tocontrol when and how a dependent station may operate. An enablingstation communicates an enabling signal, to its dependants, over theair. The enabling station may correspond to a Master (or Mode II) devicein Federal Communications Commission (FCC) nomenclature. In the abovecontext, “registered” may mean that the station has provided thenecessary information to TVWS database, (e.g. FCC Id, location,manufacturer information, and the like).

Geo-location capability may refer to the capability of a TVWS device todetermine its geographic coordinates within the level of accuracy, suchas 50 meters, as a non-limiting example.

Industrial, Scientific and Medical (ISM) bands may refer to frequencybands open to unlicensed operation, governed by Part 15 Subpart B FCCrules in the US. For example, 902-928 MHz Region 2 only, 2.400-2.500GHz, 5.725-5.875 GHz.

A Mode I device may be a personal/portable TVWS device that does not usean internal geolocation capability and access to a TV bands database toobtain a list of available channels. A Mode I device may obtain a listof available channels on which it may operate from either a fixed TVWSdevice or a Mode II device. A Mode I device may not initiate a networkof fixed and/or personal/portable TVWS devices nor may it provide a listof available channels to another Mode I device for operation by suchdevice. A Mode II device may be a personal/portable TVWS device thatuses an internal geo-location capability and access to a TVWS database,either through a direct connection to the Internet or through anindirect connection to the Internet by way of fixed TWWS device oranother Mode II TVWS device, to obtain a list of available channels. AMode II device may select a channel itself and initiate and operate aspart of a network of TVWS devices, transmitting to and receiving fromone or more fixed TVWS devices or personal/portable TVWS devices. A ModeII device may provide its list of available channels to a Mode I devicefor operation on by the Mode I device. A sensing only device may referto a personal/portable TVWS device that uses spectrum sensing todetermine a list of available channels. Sensing only devices maytransmit on any available channels in the frequency bands 512-608 MHz(TV channels 21-36) and 614-698 MHz (TV channels 38-51), for example.

TVWS bands may refer to TV channels, (in the VHF (54˜72, 76˜88, 174˜216MHz) and UHF (470˜698 Mhz) bands), where regulatory authorities permitoperation by unlicensed devices. Personal/portable devices which includeMode I, Mode II and sensing only devices, may transmit on availablechannels in the frequency bands 512-608 MHz (TV channels 21-36) and614-698 MHz (TV channels 38-51). A primary user (PU) may refer to theincumbent user of a TVWS channel.

A method and apparatus may be used for configuring silent periods acrossaggregated channels in a managed WLAN system. The use of silent periodsmay be necessary for devices that perform sensing in order to utilizeunlicensed spectrum in the TVWS bands without adversely affecting theprimary users of these bands. Silent periods may also be used todetermine the amount of interference on a TVWS band that may be causedby other secondary users outside of the managed system that may beutilizing the same channel. However, silent periods may result in areduction of the throughput over the channel. Moreover, a silent periodmay result in a delay in traffic that may affect some time sensitiveapplications such as voice-over-Internet Protocol (VoIP).

Another issue that may exist with configuring silent periods in thecontext of multiple channels is how to ensure that out-of-bandinterference does not affect sensing performed by hardware (HW) that isco-located or in close proximity of the AP or stations that may beinvolved in transmission of the managed system. In a system that useschannel aggregation, silencing all channels simultaneously during eachsilent period may be performed to reduce interference. However, thisstrategy may result in significant throughput losses and may not benecessary depending on the type of channel that needs to be sensed, thelocation radio frequency (RF) properties of the sensing HW, and themanaged communication devices.

Efficient configuration of these silent periods may be needed in asystem using aggregated channels in order to maintain the throughputgains achieved by using aggregation. Silent periods may be configured oneach of the individual physical (PHY) channels that may be used by themedium access control (MAC) aggregation scheme. The configuration ofthese silent periods may depend on multiple factors such as sensingrequirements, knowledge of which primary users each of the channels arereserved for, and location and type of sensing radio HW.

Once silent periods have been efficiently configured, they may need tobe coordinated across all nodes controlled by a central entitycoordinating the sensing and silent period configuration. Thiscoordination may require robust communication of the silent period toavoid having stations miss the silent period and result in degradedsensing results. Since a carrier sense multiple access (CSMA) system mayincur some message loss, a method and apparatus may be used for ensuringthat stations that miss a silent period indication do not adverselyaffect sensing performance.

Described herein are methods and apparatus for silent periodconfiguration and coordination. The embodiments described herein may useboth periodic and asynchronous silent periods. In order to scheduleperiodic silent periods over a set of aggregated channels, whilemaintaining channel throughput despite the presence of silent time, thesilent periods may be scheduled in a non-synchronized fashion whenpossible. This may ensure that there is at least one channel to maintainthe channel traffic on the aggregated channel link.

The description herein may use a certain number of channels forillustration purposes only. The examples and embodiments are not limitedto, for example 4 channels, and may be applicable to N channels.Although TVWS may be used for illustration purposes, the methods arefurther applicable to any form of opportunistic spectrum where sensingthrough silent periods may be required.

The silent period is applicable to sensing for detection of primaryusers and sensing for measurement of other secondary systems forcoexistence purposes.

FIG. 2 shows an example case with four channels and a channel acting asprimary channel. Channel 1 may be the primary channel 205 during themajority of the time due to the quality of this channel as compared tochannels 2, 3 and 4. Channel 2 may become the primary channel 210 duringsilent time periods 215 allocated to channel 1. FIG. 3 shows anotherexample where the choice of a primary channel 305 may be independent ofthe quality of the four channels. The role of the primary channel maychange in a round-robin fashion based on a silent period schedule 310,and may result in a scheme where the number of primary channel switchesmay be minimized.

Other examples for primary channel selection during the silent periods,such as random selection, may also be possible. Although FIGS. 2 and 3show the same silent period interval or periodicity across the fourchannels, a system may manage channels that have different sensingrequirements, and therefore a different amount of silent time in eachchannel. In this case, silent periods may be scheduled in achannel-independent fashion. The scheduling decisions, including thechoice of the alternate primary channel to be used and the use ofchannel independent silent periods, may be made by a logical entity,such as a Silent Period Management Entity.

A channel independent silent period may allow skewing of silent periodson different channels so that there may be at least one channel in theaggregated channel set that may be used by the DSM system at any giventime rather than making all channels unusable at the same time. This maybenefit transmission scenarios where the application is sensitive to adelay and also may avoid the scenario where the DSM engine may not beable to send control messages for a fixed period of time.

The channel independent silent period may allow tailoring of the silentperiod duration on each channel based on the channel type. For example,if one channel has a larger silent period duty cycle requirement thanall the other channels, the other channels may not need to bedisadvantaged by this as they may maintain their own channel duty cyclerequirements, if possible.

The potential for scheduling silent periods in a channel-independentfashion, either on all channels or a subset of channels, may depend onwhether the out-of-band interference for channels being utilized by themanaged system will cause degradation in performance in the sensing ofchannels when the silent period is scheduled on those channels. Sincethis may depend on a number of factors, such as type of sensing HW,out-of-channel and out-of-band filtering characteristics of the devicesin the managed system, type of sensing to be performed, and maximumtransmit power of the stations utilizing the channels in the managedsystems, this information may be made available to the Silent PeriodManagement Entity to determine the schedule. Rather than using a fixedschedule to reduce out-of-band interference, the Silent PeriodManagement Entity may dynamically change the schedule to create one ormore channel-independent silent periods over the maximum number ofchannels.

In addition to the use of non-synchronized and channel-independentsilent periods, throughput and delay optimizations may be achieved bymodifying the silent period schedule for periodic silent periods basedon real-time monitoring of the channel quality. This method may be usedin a single channel example as well as in aggregated channels. Thismethod is described herein the context of an aggregated channel system,however, the same method may be applied to a system that uses a singlechannel (non-aggregated) scheme.

Selection of a silent period duration and periodicity may be driven byrequirements on the amount of time needed to perform accurate sensing.This sensing may provide detection of primary users, or it may obtainsome metric of the channel quality that may be used to dynamicallyselect the best channels available from the TVWS.

In general, a required silent period duty cycle may be associated witheach channel and this duty cycle may be derived from the silent periodrequirements of each channel. A duty cycle requirement may be specifiedby giving the amount of silent time, x, per duty cycle interval, y, andmay be referred to as an x/y requirement specification. For a given dutycycle specification, there may be multiple ways to satisfy theserequirements by changing the duration and periodicity of the silentperiod on a specific channel.

FIG. 4 shows an example duty cycle requirement 400 of 2 ms/100 ms on aspecific channel. The 2 ms of silent time duration 405 may be allocatedin a single silent period over the 100 ms duty cycle interval 410. Inexample duty cycle requirement 450, 4 silent periods of 500 μs 455 maybe distributed over a duty cycle interval 460, resulting in aperiodicity of 50 ms for the silent periods. A tradeoff betweenthroughput and delay/jitter of the resulting traffic may be expectedbased on selection of either of the two schedules over the other.Stations may interrupt transmission at a specific time. This action mayreduce the throughput, not only due to the lack of transmission duringthe silent period itself, but also in the stations preparing for asilent period. A silent period in a CSMA system may be scheduled at afixed time. Some bandwidth loss may be incurred, both prior to andfollowing the silent period. This bandwidth loss may be due toabstaining from transmission of a packet if the acknowledgement (ACK) isnot received prior to the start of a silent period, or for re-accessingthe medium using CSMA following the silent period.

For fixed duty cycle requirements, when silent periods are chosen with alonger duration and longer periodicity, (for example duty cyclerequirement 400 in FIG. 4), traffic delay/jitter may be sacrificed forbetter throughput, since the number of silent periods may be reducedover a fixed interval. When shorter silent periods are chosen anddistributed over the same interval, the traffic delay/jitter caused bythe silent period may be reduced. The throughput compared to duty cyclerequirement 400 in FIG. 4, however, may be reduced as a result ofincreased channel usage reduction from switching into and out of asilent period. As a result, depending on the specific quality of service(QoS) requirement at a specific time, a different silent periodconfiguration may be desirable over another.

A method and apparatus may be used to dynamically tailor the silentperiod configuration for a given duty cycle requirement to ensure thatthe QoS on the channels that are utilized may be satisfied in the bestcase. As a result, for traffic requiring low latency/jitter, silentperiods that are in line with duty cycle requirement 450 may be used. Inthe case where the QoS requirements may dictate the need for maximumthroughput, silent periods that are in line with example 1 may be used.The silent period configuration may therefore be changed dynamicallywith time based on changing one or more QoS requirements of the trafficutilizing each of the channels. The QoS may also be involved in thescheduling of silent period duration in asynchronous silent periods bydictating the maximum silent period duration of an asynchronous silentperiod.

The method and apparatus may be used to coordinate the silent periodswith another station through the transmission of silent periodinformation in a beacon. As an aggregated beacon may be employed, thesilent period information may be transmitted in the aggregated beacon inorder to improve robustness and avoid the scenario where a station maymiss the notification of a silent period due to momentary fading. Inaddition, since the beacon may be missed by one or more stations due tomultipath issues, collisions, and hidden node problems, a beacondependant transmission may be implemented into the system to avoid theseissues. This may require all stations that do not properly receive thebeacon during a specific beacon interval to abstain from transmittinguntil the next beacon is received. Since the silent periods start timesmay be relative to the beacon times, knowledge of the exact timing of asilent period start time by each station may be dependent on thereception of the beacon that immediately precedes it. A station thatdoes not receive the beacon may be forced to be silent during the beaconinterval until the next beacon is received. This may guarantee that allstations will be silent during the silent period scheduled by thecentral entity.

The method and apparatus may also be used for providing efficient silentperiod configuration over an aggregated channel system for the DSMsystem. The method and apparatus may, however, be applied to a systemwith any architecture by assigning the logical entities described hereinto different locations.

A number of assumptions may be made to illustrate the algorithm andmessaging involved in the method and apparatus described herein. Theseassumptions should not limit the use of the method and apparatus in asystem that may not use these same assumptions. The assumptions mayinclude: 1) the use of up to 4 channels in the aggregation scheme, (inorder to illustrate the scheduling examples); 2) limitation to twopotential primary users—wireless microphone and digital television(DTV); and 3) a transmit radio for all devices in the DSM system thatcovers the TVWS using two separate wideband digital radio boards whereone board may cover the lower band of the TVWS and another board maycover the upper band of the TVWS. Each board may have strong out-of-bandinterference rejection, however, out-of-channel interference rejectionmay only meet the requirements of a TVWS transmitter.

The silent period schedule may be tied to QoS. As stated hereinabove,there may be a tradeoff between delay and throughput that relates silentperiod scheduling to QoS. Periodic spectrum sensing may be convenientfor practical implementation. In periodic spectrum sensing, in everytime interval Tp, defined as the sensing period periodicity, a spectrumsensing algorithm may run to full completion to make a decision on thepresence or absence of a primary spectrum user. A sensing duty cycle maybe the ratio of the total time spent on spectrum sensing to the timeinterval Tp. For energy detection based spectrum sensing algorithms,there may be a minimum number of samples needed for a performancetarget. Since each sample corresponds to a sampling interval, theresulting total sensing time may be fixed.

The value of Tp may be determined by the spectrum access policies andthe DSM system design, and may be fixed in practical implementations.The spectrum access policies may impose a requirement on the responsetime for the DSM system, and this requirement may dictate how oftenspectrum sensing is performed. For example, it may be required that aDSM system respond to a wireless microphone in less than 2 seconds. Theresponse time may include the time for both spectrum sensing and theevacuation of the DSM system from the channel being used by the wirelessmicrophone. In the DSM system design, if a fixed amount of time for thesystem evacuation is allocated, then the time budget left for spectrumsensing, i.e., Tp, may also be fixed.

The sensing time may be segregated into multiple time intervals whilekeeping the same sensing duty cycle. Each contiguous time interval forsensing may be termed a sensing duration and may be denoted as Td. Suchsegregation of the sensing time may offer a way to configure the sensingperiod. FIGS. 5A and 5B illustrate example relationships between Tp 500and Td 505, and sensing period configuration, where Tp=T′p (510) andTd=2*T′d (515). In FIG. 5A, the sensing duty cycle=Td/Tp, and in FIG.5B, the sensing duty cycle=2*T′d/T′p=Td/Tp.

Td may be configured based on the sensing duty cycle and a fixed valuefor Tp. The number of Td's within a Tp may be configured in a similarfashion. Such configurations may give rise to a tradeoff between delayand throughput. Assuming uniform packet arrivals and negligible packetlengths, the average packet delay may be proportional to Td. Thus, as Tddecreases, the average packet delay may decrease. On the other hand, asTd decreases, when the effects of packet lengths are considered, thefraction of time that may be useful for data transmission decreases.This decrease may be due to a contiguous time interval available fordata transmission, shown as an un-shaded time interval in FIG. 5A, thatmay not be able to fit multiple frames or transmission opportunities(TXOPs), and the time wasted as such may account for a larger portion asTd decreases. In addition, as Td decreases, the number of Td's within aTp may increase. Since there may be a new round of contention afterevery sensing operation of duration Td, there may be more contention,which may further reduce the throughput.

There may be a lower bound on the possible values for Td, and it may bedenoted as Td_min. The lower bound may occur in some applications whenthe sensing algorithm needs a minimum number of contiguous samples inorder to accomplish the sensing task, for example, the duration of apilot sequence used by the sensing algorithm.

In general, a silent period management entity (SPME) may be the maincontroller of silent periods that are used within the DSM system. Thisentity may be a medium access control (MAC) layer management entity thatmay be added to IEEE 802.11-based systems to manage the scheduling ofsilent periods, whether or not that system employs channel aggregation.

FIG. 6 shows example DSM system architecture 600 including an accesspoint (AP) architecture 605 and a station (STA) architecture 610. Inparticular, FIG. 6 shows example architecture and basic interfacesbetween the SPMEs and MAC layer components in the AP 605 and STA 610.Silent periods may be managed by each AP. For a DSM system that containsmultiple APs, the SPME for each AP may contain an additional interfacefor coordination of silent periods across the multiple APs.

The AP 605 may include a SPME 615 connected to a sensing/capabilitydatabase 620, a sensing toolbox 625, a channel management function (CMF)630, a MAC QoS entity 635 and a silent period interpretation entity(SPIE) 640. The SPIE 640 may be connected to a MAC buffering and controlentity 645, which in turn may be connected to a MAC layer/sublayermanagement entity (MLME) 650. The STA 610 may include a SPIE 655 whichmay be connected to a MAC buffering and control entity 660 and a MLME665. The MAC buffering and control entity 660 may be connected to theMLME 665. The AP 605 and STA 610 may be connected through MLME 650 andMLME 665.

The main components in the DSM system 600 are described herein. Each ofthe entities except for the sensing toolbox/processor 625 and the CMF630, may be MAC-layer management functions. They may therefore beintegrated into a more complete MLME that contains silent periodmanagement functionality. In the architecture shown in FIG. 6, theseentities may be separate from the MLME 650 to illustrate how silentperiod management may be added to an existing IEEE 802.11-based MLME.

The SPME 615 may be the main entity at the AP 305 that determines thelength and scheduling of the silent periods on each channel in a dynamicfashion. It may handle both periodic and asynchronous silent periods.The roles of this entity may be: 1) select between channel independentand channel synchronized silent periods based on interferenceinformation from the capabilities database 620 and the maximum powertransmitted by each station; 2) assign a silent period duration andperiodicity for silent periods on each channel based on QoS informationand duty cycle requirements; 3) jointly manage the scheduling of silentperiods across the four aggregated channels in an intelligent fashion;and 4) notify the SPIE 640 of a change in the silent period schedule.

The SPIE 640 may ensure that the STA 610 adheres to the rules andtimings required based on the silent period messages that are receivedat the STA 610 and interpreted by the STA 610 MLME 665. The SPIE 640 mayreceive at the AP 605 the silent period schedule derived by the SPME 615and may implement the schedule at the MAC layer 635. The SPIE 640 tasksmay include instructing the MAC buffering and control entity 645 how tobuffer, reorder, and packetize frames in order to respect upcomingsilent periods defined in the schedule. At the STA 610, the SPIE 655 mayreceive the information from the beacon as interpreted by the MLME 665.The SPIE 655 may instruct the MAC buffering and control entity 660 inthe same way in order to implement the silent period from the station'sperspective.

The sensing toolbox/processor 625 may coordinate the sensing of theutilized channels for determining the presence of interference orprimary users (as applicable). It may control the sensing HW for anydedicated sensing boards, or sensing HW that may be located at the DSMclients.

The MAC QoS 635 may provide QoS services to the system 600 at the MAClayer. Its role, relative to silent periods, may be to provide inputs onthe maximum allowable silent period duration, (for asynchronous silentperiods), and to dynamically maintain the best efficiency for the silentperiods in terms of the traffic type and QoS instructed by the higherlayers.

The MAC buffering and control entity 645 and 660 may provide transmitbuffering services, such as reordering, frame size adjustment based onchannel properties and the like for the aggregated channel MAC.

The MLME 650 and 665 may be a standard MAC layer management entity as inIEEE 802.11-based systems, and may include enhancements for the supportof silent periods as described herein. Some enhancements may involve theability to interact with a MAC layer interpretation entity (not shown)and a MAC buffering and control entity, such as 645 and 660.

The CMF 630 may be the main channel selection and channel managemententity in a DSM engine.

The sensing/capability database 620 may be the main repository fordevice capabilities. For the purposes of silent period, the informationof interest in database 620 may be the sensing capabilities of the radiofrequency sensing board (RFSB) and the out-of-band and out-of-channelinterference properties of the AP and devices in the DSM system. Thisinformation may be entered into the sensing/capability database 620during the attach procedure. It is then used by the SPME 615 to schedulechannel-independent silent periods where possible.

Described herein are the different messages that may be exchanged acrosseach interface in the architecture of FIG. 6, as well as the contents ofthese messages. The S1 interface may be used to indicate the channelscurrently used for aggregation by the AP 605 in the DSM system 600 andany properties of these channels required by the SPME 615 fordetermining the silent period schedule. It may also be used tocommunicate the silent period duty cycle requirements to the SPME 615.Table 1 shows some examples of S1 interface messages.

TABLE 1 Message Name Originator Description CHANNEL_CONFIG CMF Sent bythe CMF to indicate the channels to be used by the AP for communicationwith the associated stations/clients. A CHANNEL_CONFIG may also be usedto reconfigure or remove a channel from the channels to be aggregatedCHANNEL_CONFIG_CONF Silent Confirms a Period CHANNEL_CONFIG messageManagement Entity SET_SILENT_PERIOD_REQUIREMENTS CMF Sets the requiredduty cycle for periodic silent periods when determining the presence ofDTV, or wireless microphone, as well as the current duty cycle needs forsensing for channel quality determination. These requirements may bedependent on the sensing hardware capabilities available to the sensingprocessor, such as the number of devices performing sensing, theprocessing power of each device, etc. This information may be obtainedfrom the sensing processor through message communication, or may bemanaged by the CMF. SET_SILENT_PERIOD_REQUIREMENTS_CONF Silent Confirmsthe Period SET_SILENT_PERIOD_REQUIREMENTS_CONF Management Entity MessageName Message Contents CHANNEL_CONFIG numChannel - Number of channelsfreqs - List of channels and their associated frequency range EIRP -List of maximum EIRP that can be used on each channel dbInformation -Enumeration type indicating the information obtained about this channelfrom the TVWS database (a channel may be free, reserved for DTV,reserved for wireless microphone, or reserved for both)CHANNEL_CONFIG_CONF statusCode - Success or reason code for failureSET_SILENT_PERIOD_REQUIREMENTS dtvDetectionCycle - Required duty cycleneeded for accurate DTV detection within timing requirements (in dutycycle of x ms per 100 ms, or x ms per interval of 100 ms).wmDetectionCycle - Required duty cycle needed for accurate wirelessmicrophone detection within timing requirements (in duty cycle of x msper 100 ms, or x ms per interval of 100 ms). channelQualDutyCycle -Required duty cycle needed for channel quality measurements (in dutycycle of x ms per 100 ms, or x ms per interval of 100 ms).SET_SILENT_PERIOD_REQUIREMENTS_CONF statusCode - Success or a reasoncode explaining the failure.

The S2 interface may be the interface used to communicate the need forasynchronous silent periods, (as determined by the sensing processor625) to the SPME 615. Table 2 shows some examples of S2 interfacemessages.

TABLE 2 Message Name Originator Description Message ContentsASYNCHRONOUS_SILENT_PERIOD_REQ Sensing Message from the channelIDs -List of Processor Sensing Processor to channel(s) on which the SilentPeriod sensing needs to be Management Entity to performed request anrequestedDuration - asynchronous silent Silent period length period.requested by the sensing processor ASYNCHRONOUS_SILENT_PERIOD_CONFSilent Period Message confirming numDistinctSilentPeriod - Managementthe silent period The number of Entity request and indicating distinctsilent periods the number of distinct into which asynchronous silentrequestedDuration periods into which the has been split (arequestedDuration has value of 0 indicates a been divided. The failureto schedule an actual silent period asynchronous silent may start withthe period) SILENT_PERIOD_START_MESSAGE duration - Duration sent of eachdistinct silent on the S8 interface period.

The S3 interface may be used to communicate the silent period scheduleand dynamic changes in the schedule to the SPIE 640 that may implementthis schedule in the MAC layer. Due to the assumption of a dual-bandradio for all devices, the contents of the messages may be specific tothis assumption. For a system with general radio assumptions, themessage contents may change. Table 3 shows some examples of S3 interfacemessages.

TABLE 3 Message Name Originator Description Message ContentsPERIODIC_SCHEDULE_CONFIGURE Silent Period Schedule of periodicgroup1SilentRange - Management silent periods to be Range of frequenciesthat Entity implemented on the four can be sensed for group 1 channelsas decided by (to be passed to the the Silent Period sensing processor)Management Entity. group2SilentRange - This message may be Range offrequencies that sent each time a new can be sensed for group 2 silentperiod (to be passed to the configuration is sensing processor)determined by the Silent group1Duration - Period Management Duration ofsilent period Entity. for channels in group1. This may be a list ofdurations, in the case where multiple silent periods may be required oneach channel (see scheduling examples) group1Periodicity - Periodicityof silent period for channels in group 1. This may be a list ofperiodicities, in the case where multiple silent periods may be requiredon each channel (see scheduling examples). group2Duration - Duration ofsilent period in for channels in group 2 (empty if no channels ingroup2). This may be a list of durations, in the case where multiplesilent periods may be required on each channel (see schedulingexamples). group2Periodicity - Periodicity of silent period for channelsin group 2 (empty if no channels in group 2). This may be a list ofperiodicities, in the case where multiple silent periods may be requiredon each channel (see scheduling examples).ASYNCHRONOUS_SILENT_PERIOD_IND This message indicates appliedGroups -Channel the immediate need to groups to which the configure anasynchronous silent period asynchronous silent applies period on one ormore duration - Duration group. The Silent of each asynchronous PeriodInterpretation silent period in ms entity of the AP may numAsync -Number automatically suspend of asynchronous silent transmitting periodsto send in a information concerning row on the the periodic silentperiod appliedGroups for this channel until timeSeparation - theasynchronous silent Separation in time period has been betweencompleted. At that time, asynchronous silent the Silent Period periodsInterpretation Entity may resume the regular periodic silent period fromwhere they left off.

The S4 interface may be used to limit the silent period durations basedon the measured and targeted QoS. It may focus predominantly on limitingthe length of the silent periods to ensure the end-to-end delay islimited over each channel. At system initialization, the default silentperiod duration may be configured while maintaining the required dutycycle. For example, the duty cycle may be satisfied with a single silentperiod. As clients join, the QoS may request the SPME 615 to decreasethe duration, (increase the periodicity), of the silent periods. Table 4shows some examples of S4 interface messages.

TABLE 4 Message Message Name Originator Description ContentsDELAY_CHANGE_REQ MAC Layer Request message by the modifyType - QoS MAClayer QoS block to Increase or reduce or increase the block decreasedelay experienced by a channelList - specific channel(s) as a List ofchannel result of a silent period. For where delay may this design, eachmessage be increased. may request an increase or decrease in the lengthof the silent periods by 50%. The result of the attempt may becommunicated in the DELAY_CHANGE_RESP DELAY_CHANGE_RESP Silent PeriodResponse to the statusCode - Management DELAY_CHANGE_REQ Success or aEntity indicating whether a change reason code in silent periodexplaining the configuration request could failure. be satisfied.SILENT_AMOUNT_CHANGE_REQ MAC Layer Request to change the modifyType -QoS amount of silent time for a Increase or channel of type “Free”. Thisdecrease message may not be applied channelList - to any channels whereList of channel sensing for primary users is where delay may beingperformed, since these be increased. channels may keep the silent periodduty cycle fixed. SILENT_AMOUNT_CHANGE_RESP Silent Period Response tothe statusCode - Management SILENT_AMOUNT_CHANGE_REQ Success or a Entityindicating whether reason code a change in silent period explaining theconfiguration requested may failure. be satisfied.MAX_ALLOWABLE_ASYNC_DELAY_REQ Silent Period Sent by the Silent PeriodchannelList - Management Management Entity to List of channels Entityobtain the maximum that require the allowable silent period silentperiod. duration for an asynchronous silent period requested by thesensing processor. MAX_ALLOWABLE_ASYNC_DELAY_RES MAC Layer Response tothe maxDelayVal - QoS MAX_ALLOWABLE_ASYNC_DELAY Maximum delay in ms.minSeparation - Minimum separation time between asynchronous silentperiods if the requested silent period is split into multiple pieces.

The S5 interface may communicate the presence of a silent period and therequired action to be taken by the Buffering and Control Entity in orderto ensure data transmission on each of the aggregated channels may bemaintained efficiently despite the presence of silent periods. Thisinterface may exist both at the AP 605 and the STA 610 and is identicalin each case. Table 5 shows some examples of S5 interface messages.

TABLE 5 Message Message Name Originator Description ContentsSILENT_PERIOD_ARRIVAL Silent Period Notifies the duration -Interpretation Buffering and Duration of the Entity Control Entityupcoming silent of an upcoming period silent period timeExpected - thatmay Expected time require when the silent reordering period will occurand/or (this may be an modification of approximation frame since theMLME fragmentation may maintain to ensure the exact timing). buffersremain When a value of equal length. 0 is sent, this This message meansthat the may be the silent period has same for the already begun. S5interface on channelsAffected - the AP and the The list of PHY station.In the channels that case of an may be silenced. asynchronous silentperiod, the message may be sent with little or no advanced notice(depending on whether we are on the AP or station side respectively).

The S6 interface may be used by the SPME 615 to obtain information aboutthe sensing capabilities and transmit/receive (TX/RX) radio capabilitiesof the AP 605 and STAs 610 in the DSM system 600. Using thisinformation, the SPME 615 may determine which radio bands may be sensedsimultaneously while normal data transmission is occurring on otherbands. Table 6 shows some examples of S6 interface messages.

TABLE 6 Message Message Name Originator Description ContentsGET_SENSING_RADIO_CAPABILITIES Silent Period Sent to request informationNone Management Entity about the sensing radio capabilities andrestrictions that may affect the silent period configurationsSENSING_RADIO_GETCAPABILITIES Sensing/Capability Response to thegroup1Dependency Database GET_SENSING_RADIO_CAPABILITIES Range - messageRange of channels in the first dependency group group2Dependency Range -Range of channels in the second dependency group.

The S7 interface may include MLME service access point (SAP) primitivesto implement the silent periods through beacon and control messages. Atthe AP 605, the SPIE 640 may indicate to the MLME 650 the timing of thesilent periods, (periodic and asynchronous), so that this timing may beincorporated appropriately in the beacon and control messages sent tothe stations. At the station, the MLME 650 may interpret the beacon andcontrol frames and send all silent period scheduling information to theSPIE 640. Table 7 shows some examples of S7 interface messages.

TABLE 7 Message Message Name Originator Description ContentsMLME_SILENT_SCHEDULE_CONFIGURE Silent Period This primitivechannelGroup1 - Interpretation may set up List of Entity beacon channelsinformation for associated with periodic silent the first periods ineach of synchronous the channels. silent period. This group may bedecided by the Silent Period Management Entity based on several inputs(see call flows) channelGroup2 - List of channels (up to 3) associatedwith the second synchronous silent period. This group may be empty.MLME_SILENT_PERIOD_START MLME Sent by the None MLME to indicate theexact starting time of a silent period. MLME_START_ASYNC_PERIOD SilentPeriod MAC layer duration - Interpretation primitive that RequiredEntity requests the duration of the MLME to start silent period anasynchronous moreFlag - silent period and Whether more consequentlyasynchronous suspend any silent periods synchronous are expected orsilent periods if periodic silent that may be periods may be occurringon the rescheduled same frequency. following this asynchronous silentperiod. phyChannels— C List of PHY channels on which the asynchronoussilent period applies. MLME_QUIET_INFORMATION MLME This message Thequiet may be used at information the station only. element on each Itmay send the of the channels quiet information may be received receivedin the (see section beacon to the TBD for Silent Period details).Interpretation Entity for management of the timing of the silentperiods.

The S8 interface may carry the timing information about the silentperiods, (exact start time, duration, and bands), so that the sensingprocessor 625 may know when a sensing operation for a specific channelor set of channels should be started. Knowledge of this exact timinginformation may be ensured by a message from the MLME 650 to the SPIE640 across the S7 interface. Table 8 shows some examples of S8 interfacemessages.

TABLE 8 Message Message Name Originator Description ContentsSILENT_PERIOD_INFORMATION Silent Period Indicates to the freqRanges -Interpretation Entity Sensing Processor Range of the properties of anfrequencies upcoming silent (delimited period message. by start and Thismessage may end be sent some time frequencies). prior to the duration -occurrence of the silent silent period to allow period confirmation.duration applicable to freqRange (each silent period start message maybe associated with a single duration time)SILENT_PERIOD_INFORMATION_CONFIRM Sensing Processor Confirms the receiptstatusCode - of the silent period Success or information a reasonmessage. code explaining the failure. SILENT_PERIOD_START_MESSAGE SilentPeriod Indicates the exact None Interpretation Entity starting time ofthe silent period

The S9 interface may be used to communicate the silent periods from theAP 605 to each of the STAs 610. This interface may be implementedthrough information in the beacon and control messages.

The following call flow examples describe the main messages and theiruses in the different scenarios where the silent period management mayoccur. FIGS. 7A and 7B are flow diagrams of an example systeminitialization and silent period initiation method 700. A DSM system mayinclude interaction between a sensing processor 702, a CMF 704, a SPME706, a SPIE 708, a MLME 710, a MAC buffering and control entity 712 anda sensing/capabilities database 714.

When the DSM system boots up (720), the SPME 706 may receive the silentperiod requirements for each type of primary user interference (722) andsend a confirmation (724). This information may guide the SPME 706 increating the silent period schedule. When the CMF 704 selects thechannels to be used by the system (726), it may send a CHANNEL_CONFIGmessage across the S1 interface to the SPME 706 (728), which in turn maysend a confirmation (730). This message may also include additionalinformation about the type of sensing that may be performed based on thedbInformation parameter within the message (732). If the channel isfree, based on the TVWS database, this channel may be used as a channelused in a Mode I and a Mode II operation. If the channel is consideredoccupied, then it may be used by a sensing only mode device and primaryuser detection may be required. If additional information is presentfrom the TVWS database, (whether the primary user is known to be sensingonly or DTV), that may be reflected in this parameter.

The SPME 706 may generate a schedule based on the default settingsrelated to QoS (734) and may send this schedule to the SPIE 708 (736).This schedule may then be sent to the MLME 710 through an MLME primitive(738) so that the MLME 710 may begin to include this information withinthe beacon (740).

At some time delta prior to the arrival of a silent period (742), theSPIE 708, which may be maintaining the latest schedule, may notify theMAC buffering and control entity 712 so that it may adjust its framebuffering rules for the arrival of a silent period (744). Informationabout the upcoming silent period may be sent to the sensing processor702 (746), which in turn may send a confirmation (748).

The MLME 710 may determine the start of the silent period based onknowledge of the beacon timing for silent periods starting immediatelyfollowing the beacon, or based on the target transceiver unit (TU) ofthe silent period for silent periods occurring within the beaconinterval (750). When the silent period time arrives, the MLME 710 maydisable the channels affected by the silent period within the EnhancedDistributed Channel Access (EDCA) algorithm (752) and may send a messageto the SPIE 708 (754) that may be forwarded to the sensing processor 702for synchronizing the sensing operation (756). Depending on theimplementation, advanced notice may be sent in order to account formessaging latencies with the sensing processor 702. After the silentperiod ends, the MLME 710 may re-enable the channels affected by thesilent period within the EDCA algorithm (758). This may be done for eachsilent period.

FIG. 8 is a flow diagram of an example channel reconfiguration 800performed by a CMF 804 in a DSM system. The DSM system may includeinteraction between a sensing processor 802, a CMF 804, a SPME 806, aSPIE 808, a MAC QoS 810, a MLME 812 and a MAC buffer and control entity814.

The CMF 804 may decide to change the active channels for various reasonsduring operation of the DSM system (820). The change in channels mayinvolve a change in the active channels used by the aggregation, or adecrease in the channels followed by an eventual increase when a newavailable channel is found. In each case, the CMF 804 may send aCHANNEL_CONFIG message with a new set of active channels to the SPME 806(822), which in turn may send a confirmation (824). The SPME 806 may beresponsible for re-computing a new silent period schedule for theperiodic silent periods (826). When the new silent period schedule hasbeen sent to the SPIE 808 (828), the SPIE 808 may decide the best newtime to have the new schedule take effect (830). This may result in thedelay of the MLME_SCHEDULE_CONFIGURE primitive until an upcoming silentperiod occurs (832). The delay may occur if that silent period is lessthan the delta from the reconfiguration time, or if sensing informationmay be obtained from the upcoming silent period, such as, for example,alternate channel sensing information. After the delay lapses, the SPIE808 may send the MLME_SCHEDULE_CONFIGURE primitive to the MLME 812(834), which in turn may modify the information sent in the beaconaccording to the new schedule (836).

FIGS. 9A and 9B are flow diagrams of an example asynchronous silentperiod configuration method 900. The DSM system may include interactionbetween a sensing processor 902, a CMF 904, a SPME 906, a SPIE 908, aMAC QoS 910, a MLME 912 and a MAC buffer and control entity 914.

During communication between the CMF 904 and the sensing processor 902for channel selection/evaluation (922 and 924), the sensing processor902 may decide that an asynchronous silent period is required (926). Anasynchronous silent period may be required where a channel is evacuateddue to a primary user or strong interference, and an alternate channelis not yet available. In order to speed up the selection of a newchannel for the system, the sensing processor 902 may request anasynchronous silent period to perform sensing on alternate channels(928). The SPME 906 may check this request with the MAC QoS entity 910(930) to determine the maximum allowable silent period that isacceptable for a given channel (932). Based on the maximum allowabledelay and, optionally, the minimum time between two asynchronous silentperiods having that delay sent by the MAC QoS entity 910 (934), the SPME906 may split the requested silent period from the sensing processor 902into multiple asynchronous silent periods (936). This information may besent to the sensing processor 902 (938) as well as the SPIE 906 (940).

The SPIE 908 may cancel any ongoing periodic silent periods for theaffected channels within the maintained schedule (942) and begin aprocedure for starting a silent period with the MAC buffer and controlentity 914 (944) and MLME 912 (946). The MLME 912 may disable theperiodic silent period on any affected channels as requested by the SPIE908 at the receipt of the first MLME_START_ASYNC_PERIOD primitive (948).The MLME 912 may disable the channels affected by the silent periodwithin the Enhanced Distributed Channel Access (EDCA) algorithm (950)and may send a message to the SPIE 908 (952) that may be forwarded tothe sensing processor 902 for synchronizing the sensing operation (954).Depending on the implementation, advanced notice may be sent in order toaccount for messaging latencies with the sensing processor 902. Afterthe silent period ends, the MLME 910 may re-enable the channels affectedby the silent period within the EDCA algorithm (956). The MLME 912 mayalso re-enable periodic silent periods on these channels after the lastasynchronous silent period is received (958). The MLME may keep track ofwhen the control frame has been sent by the physical (PHY) entity andmay trigger the MLME_SILENT_PERIOD_START primitive to the SPIE 908accordingly.

FIG. 10 is a flow diagram of an example QoS requirement change method1000. The DSM system may include interaction between a sensing processor1002, a CMF 1004, a SPME 1006, a SPIE 1008, a MAC QoS 1010, a MLME 1012and a MAC buffer and control entity 1014.

The MAC QoS entity 1010 may determine based on delay or throughputcharacteristics on certain channels that the configuration of the silentperiod may need to be changed (1020). In general, for a given duty cyclerequirement, when the duty cycle requirement is satisfied using longersilent periods, the overall throughput may be greater but theapplication delay may also increase. On the other hand, when more andshorter silent periods are used, the application delay may be smallerbut the overhead at the MAC layer or entity, (due to traffic pausing andrestarting), may cause degradation to the overall throughput. The silentperiod duration may be managed in such a way as to optimize the QoSbased on measurements made at the MAC QoS entity 1010. The MAC QoSentity 1001 may indicate to the SPME 1006 when it requests an increaseor decrease in the delay (1022). The SPME 1006 may create a new schedulefor the periodic silent periods based on this request (1024), ifpossible and may send a DELAY_CHANGE_RESP message to the MAC QoS entity1010. The SPIE 1008 may receive the new schedule (1028) and may thendetermine the best time for implementing the new schedule (1030). TheSPIE 1008 may wait for a silent period to pass (1032) and may then senda MLME_SCHEDULE_CONFIGURE message to the MLME 1012 (1034), which in turnmay modify the information being sent in the beacon in accordance withthe new schedule (1036).

FIG. 11 is a flow diagram 1100 of an example for using messages at DSMclients and/or stations. The call flow example in FIG. 11 illustratesthe messages used in the case of both periodic and asynchronous silentperiods. The entities at a DSM client may include a SP IE 1105, a MLME1110, and a MAC buffering and control entity 1115. These entities maycommunicate using a reduced set of messages that may be defined overeach interface. DSM clients may be aware of the presence of a silentperiod based on the arrival of beacon and control messages in the formof management frames received by the station MLME 1110 (1120). The MLME1120 may send the silent period information to the SPIE 1105 (1125),which in turn may send a SILENT_PERIOD_ARRIVAL message to the MAC bufferand control entity 1115 (1135) when a silent period is about to start(1130). The SPIE 1105 may receive a MLME_SILENT_PERIOD_START message(1135) when the silent period starts (1140) and may update timing basedon exact beacon arrival (1145).

With regard to asynchronous silent periods, DSM clients may be aware ofthe presence of a silent period based on the arrival of an asynchronoussilent period control message in the form of management frames receivedby the station MLME 1110 (1150). The SPIE 1105 may receive aMLME_SILENT_PERIOD_START message (1155), cancel pending synchronoussilent periods associated with this channel for this beacon interval(1160) and may send a SILENT_PERIOD_ARRIVAL message to the MAC bufferingand control entity 1115 (1165).

As described herein, the SPME schedules silent periods. Based on thecall flows described herein, a scheduling algorithm such as the creationof a schedule based on all available information, may be performed atthe SPME at several instances in time. This algorithm may first processthe information that is obtained from the capabilities database togenerate the rules that it may use to define the schedule. These rulesmay remain fixed, unless they depend on the arrival of a new device withsensing capability or transmission (TX) band properties that may changethe out-of-band interference assumptions.

Given this set of scheduling rules, the SPME may create a schedule forthe silent periods for each of the channels each time the followingevents occur: 1) the CMF may change the channels utilized by the systemand the current silent period schedule may be changed to avoidinterference from transmitting stations affecting the sensing results;2) the duty cycle requirements from the sensing toolbox may have beenchanged due to the arrival of a new device with sensing capability, (orthe departure of a sensing device; and 3) the current QoS requirementsof the utilized channels may have changed and the current silent periodschedule may not give the best QoS performance for the new requirements.

Silent periods may be scheduled using the required duty cycle for eachtype of channel. When a required duty cycle is specified, the SPME mayensure that the amount of sensing time specified by the duty cycle maybe allocated in terms of silent time. In order to simplify the silentperiod scheduling, duty cycles indicated in theSET_SILENT_PERIOD_REQUIREMENTS message may be given in terms of time per100 ms or time per multiple of 100 ms. For example, 5 ms/100 ms, 1ms/100 ms and 10 ms/300 ms are valid duty cycles.

In order to link a duty cycle with each of the channels, a particularchannel may be associated with a channel type. This channel type may besent to the SPME with each CHANNEL_CONFIG message. An example of each ofthe channel types that may be associated with a TVWS channel is shown inTable 9. Some arbitrary duty cycle requirements are shown to indicatehow these requirements may be attached to each channel by the sensingprocessor, (through the SET_SILENT_PERIOD_REQUIREMENT).

TABLE 9 Channel Type (from the dbInformation Channel Type ID parameter)Duty Cycle Requirement Channel Type 1 Reserved for 2 ms/100 ms WirelessMicrophone Channel Type 2 Reserved for DTV 2 ms/100 ms Channel Type 3Reserved for DTV 4 ms/100 ms and Wireless Microphone Channel Type 4 FreeNo requirement (default is 1 ms/1000 ms)

By default, the SPME may allocate the duty cycle requirement in a singleportion of silent time, as shown in FIG. 12. Based on the hypotheticalvalues in Table 9, a silent period 1200 of duration 2 ms may occur witha period 1205 of 100 ms for a channel reserved for a wirelessmicrophone, for example. Other silent periods 1210, 1215 and 1220 maydepend on type of channel reservation or free channel status.

Silent periods allocated by the SPME over the four aggregated channelsmay be either channel synchronous or channel independent. When channelsynchronous silent periods are used, all four channels may exhibit asilent period simultaneously. This means that the duration andperiodicity of the silent periods on all channels may be the same. Whenchannel independent silent periods are used, there may be one or morechannels that may be performing data transmission, while one or moreother channels may be performing a silent period.

In channel synchronous silent periods, the silent periods of allchannels may match the worst case duty cycle of the four channels. Thechange in silent period configuration that may be commanded by the MACQoS entity may apply to all of the four channels. For example, if theMAC QoS entity requests a decrease in delay, and the worst case dutycycle required is that of wireless microphone, the silent periods maychange from 2 ms every 100 ms to 1 ms every 50 ms, for example, and thismay occur on every channel. A minimum silent period duration may beadhered to for each channel type. This minimum may be dependent on thesensing hardware, and may be provided in theSET_SILENT_PERIOD_REQUIREMENTS message. Channels that do not have a dutycycle requirement, for example a channel of type “Free” as definedhereinabove, may have silent periods cancelled as determined by the MACQoS entity.

An example implementation for the SPME may be based on some hypotheticalassumptions to illustrate application of the methods describedhereinabove. A wideband digital radio may be assumed for both device andAP transceiver (TRX) operations as well as for sensing operations. Itmay be assumed that the radio that performs the sensing is a differentradio than the AP TRX radio, and may or may not be collocated with theAP. The digital radio may include two separate radio boards: a low-bandboard that may transmit over the 512-608 MHz frequency range and ahigh-band board that may transmit over the 614-698 MHz frequency range.Analog filtering may be applied only on a band basis, for example lowband or high band. As a result, transmission on any TVWS channel in thelow-band may create interference over the entire low band, and thisinterference may be limited only to the out-of-band transmissionrequirements of adjacent TVWS channels that may be ensured by digitalfiltering. This interference may create problems with sensing ofwireless microphone and DTV signals, where the requirement is to detectsignals below the noise floor, even when this sensing may be performedby a separate radio. As a result, sensing for wireless microphone andDTV signals may require a silent period that is “band-wide” such thatthe silencing is of the entire low-band or high-band and may depend onthe location of the channel on which sensing is being performed.

The requirement of band-wide silencing may depend on the followingfactors. If wireless microphone or DTV sensing must be performed on aparticular channel, transmission on other channels that are in the sameband, (low-band or high-band), may need to be silenced as well. Thedecision on the necessity of silencing the other channels may depend onthe second factor. In the case of sensing a channel of type “Free”,where only channel quality may be required, this may be performedwithout the need for silencing other channels within the same band. Theexpected interference caused by a separate sensing radio may be belowthe sensitivity of a WiFi terminal (˜−85 dbm). If the sensing radiobeing used is far enough from all of the devices transmitting, theinterference created by the devices that are transmitting in thevicinity may be below the detection level of wireless microphone andDTV. In this case, independent silent periods may be used.

The information needed to distinguish the scenario based on the abovetwo factors may reside in the capabilities database that is read by theSPME. It may be assumed that the SPME has made this decision and thesilent period configuration is chosen accordingly.

The following scenarios illustrate the potential silent period schedulesmaintained and controlled by the SPME. The durations and periodicityvalues used in the illustrations serve only as examples to show how theschedule is derived based on the channel type, the allocation ofchannels to each radio band, and dynamic requests from the MAC QoSentity. The rules used by the SPME in each scenario are listed in Table10.

TABLE 10 Rule Description Duty Cycle For all channel types except“Free”, the minimum duty cycle requirement may be maintained. For achannel of type “Free”, the duty cycle may be changed with commandscoming from the QoS Entity. Silent Period Distribution The distributionof all silent period may be such that all silent periods (independent orsynchronous) may be evenly distributed over a cycle so that the SensingProcessor will have a maximum amount of post- processing time availableto it. Dependence of Silent Periods When silent periods on differentchannels need to be channel synchronous due to interferenceconsiderations, all dependant channels may inherit the silent periodduration and timing of the channel with the worst case duty cyclerequirements. All channel types may inherit the silent period timing ofChannel Type 1. Channel Type 4 may inherit the silent period timing ofboth Channel Type 2 and Channel Type 3 as well. When a change in thesilent period configuration is requested by the MAC Layer QoS, that sameconfiguration change may be applied all channels that have channelsynchronous silent periods. Behavior during When a DELAY_CHANGE_REQ oftype DELAY_CHANGE_REQ. decrease is received, the silent period(s) for aparticular channel and its dependant channels may be split into twoequal portions and redistributed to maintain the Silent PeriodDistribution Rule. When a DELAY_CHANGE_REQ of type increase is received,silent periods for the channel may be merged in pairs to return to theconfiguration for that channel that existed prior to previous decreaserequests. Behavior during This message may have an effect only onSILENT_AMOUNT_CHANGE_REQ Channel Type 4. When a SILENT_AMOUNT_CHANGE_REQis received, each silent period duration may be either doubled(increase) or halved (decrease). A decrease request made when the silentperiod is the minimum required value may cancel the silent periods. Anincrease request made on a channel where the silent periods have beencancelled may introduce a silent period of the minimum required with aperiodicity of 1000 ms.

FIG. 13 is a diagram of an example scenario where there may be fullyindependent silent periods. This scenario may occur in the situationwhere either the sensing radio is far enough that the interferencecaused by the transmitters do not impede wireless microphone or DTVdetection, or in the situation where all channels are of type “Free”. Inthis case, the SPME may maintain a separate schedule on each of the fourchannels. Requests by the MAC QoS entity to increase or decrease thedelay on any particular channel or channels may affect the schedule onlyon that channel or channels and not on the other channel. In particular,the Channel 2 delay may be decreased from 1 ms to 0.5 ms.

The example illustrated in FIG. 13 assumes silent periods 1300 withduration of 1 ms with periodicity of 1000 ms, (the default scenario forchannels of type “Free”). A similar scheduling may occur for differentvalues of silent period duration and periodicity. Because of the use ofindependent silent periods, a primary channel switch may occur duringthe silent period for Channel 1 so that Channel 2 may be temporarilyused as the primary channel during this time. As shown, when independentsilent periods are used, the skew of the silent periods over thedifferent channels may be such that the silent periods are evenlydistributed over the 1000 ms period.

FIG. 14 is a diagram of an example scenario where there may be twoindependent channel sets. This scenario may occur in the situation wherethe “far sensor” assumption does not apply. Two independent channel setsmay be required if two channels are allocated in the low-band and twochannels are allocated in the high-band. In addition, at least one ofthe two channels in the low-band range may require sensing of wirelessmicrophone or DTV, and similarly with at least one of the channels inthe high-band range. Although one or more channels may be of type “Free”and therefore require only quality measurements for that channel, thatchannel may inherit the silent period duration and periodicity of thechannel requiring sensing of wireless microphone or DTV, as described inthe Rule on Channel Dependence. The specific example in the scenario inFIG. 14 shows two dependent channels matched to the Channel Type 1 dutycycle requirements, (i.e., Channels 1 and 2 having a silent period 1400of 4 ms. over a period 1410 of 100 ms), and two dependent channelsmatched on the Channel Type 2 duty cycle requirements, (i.e., Channels 3and 4 having a silent period 1415 of 2 ms). In this example, a temporaryprimary channel change may occur during the shaded region in the ChannelType 1 channels to the Channel Type 2 channels.

The scenario of two independent channel sets may also occur when onechannel is allocated in the high band and three channels are allocatedin the low-band, or vice-versa. For this case to fall in this scenario,at least one of the channels in the band where the three channels havebeen allocated may require sensing of wireless microphone or DTV, thusrequiring these three channels to be independent. The behavior of theSPME may be similar to the example shown in FIG. 15, where three of thefour channels may exhibit channel synchronous silent periods.

FIG. 15 is a diagram of an example scenario where there may be threeindependent channel sets. This scenario may require the “far sensor”assumption to not apply. This scenario may occur when two channels ofChannel Type 4 are allocated in the same radio band, (i.e., channels 1and 2 having a silent period 1500 and period 1510), while two otherchannels (one of which is not type 4) are allocated in the other radioband, (i.e., channels 3 and 4 having a silent period 1515 and period1520). The two channels in the first band may form two channels thathave independent silent periods. The two channels in the second band mayform a dependent channel set, but may be independent from each of thechannels in the first set.

FIG. 16 is a diagram of an example scenario where there may be fullychannel synchronous silent periods 1600. 1605, 1610 and 1615. In thisscenario, all four channels may require dependent silent periods. Thisscenario may occur in the case where the “far sensor” assumption doesnot apply, and all four channels may be allocated in the same radioband. In this case, the silent period duration and periodicity for allfour channels may match the duration and periodicity of the channel withthe highest silent period requirements. In this scenario, a switch ofthe primary channel may not be possible. As a result, the entireaggregated channel may be busy for the duration of the silent periodtime.

The MAC QoS entity may be designed for optimizing silent periods. Therequirements for adapting the silent periods for PU detection and SUdetection, (or channel quality), may be different. SU detection mayoccur for channels that are free of PUs, and it may provide informationon the quality of the channel where sensing is being performed. For PUdetection, for practical purposes, the silent period duty cycle may befixed. However, there may not be such a restriction for SU detection.

Described herein are example signal exchanges between a MAC QoS entityand a SPME for PU detection. To support dynamic silent periodconfiguration, the S4 interface may be used as described hereinabove.There may be a number of approaches that may be used, and each approachmay differ in the way that it uses the DELAY_CHANGE_REQ message.

A first approach may use a one-time specification. In this approach, theQoS module may determine the desired value for Td for achieving desireddelay and throughput performance, and send the desired value in theDELAY_CHANGE_REQ, (one-time value), message. However, the relationshipbetween Td and the delay and throughput performance may be affected bythe protocol behavior and the traffic condition, and may be difficult tobe accurately captured. Therefore, this first approach may be moredifficult to implement. However, it may allow for a more accuratespecification of the required silent period schedule and reduce themessaging overhead.

FIG. 17 is an example call flow 1700 of a signal exchange between a MACQoS entity 1705 and a SPME 1710 for PU detection. The call flow may beapplicable to a second approach where probing may be used with a changein an absolute amount. The MAC QoS entity 1705 may determine the desiredvalue for Td for achieving desired delay and throughput performance(1720) and may then send a DELAY_CHANGE_REQ, (i.e., an increase ordecrease), to the SPME 1710 (1725). The SPME 1710 may increase/decreasethe silent duration by a certain amount of time, for example, n ms. Forexample, Td←Td−n or Td←Td+n. The SPME 1710 may send a DELAY_CHANGE_RESPmessage to confirm whether the requested increase or decrease hasoccurred (1730). The MAC QoS entity 1705 and SPME 1710 may repeat thesemessages (1735) until the desired delay and throughput values areobtained (1740).

The example call 1700 may also be applicable for a third approach thatmay use probing and a change in a relative amount. The MAC QoS entity1705 may determine the desired value for Td for achieving desired delayand throughput performance (1720) and may then send a DELAY_CHANGE_REQ,(i.e., an increase or decrease), to the SPME 1710 (1725). The SPME 1710may decrease/increase the silent duration by a certain fraction, forexample, Td←Td(1−v) or Td←Td(1+v), where v may be the fraction ofdecrease/increase. The SPME 1710 may send a DELAY_CHANGE_RESP message toconfirm whether the requested increase or decrease has occurred (1730).The MAC QoS entity 1705 and SPME 1710 may repeat these messages (1735)until the desired delay and throughput values are obtained (1740). WhenTd is changed, the number of Td's within a Tp may be changed to keep thesensing duty cycle the same.

Described herein are example signal exchanges between a MAC QoS entityand a SPME for SU detection. In contrast to the PU detection example,there may be no restriction on the silent periods for SU detection.There may be a number of approaches, and each approach may differ in theway that it uses the SILENT_AMOUNT_CHANGE_REQ message.

A first approach may use a one-time specification. In this approach, theMAC QoS entity may determine the desired value for the silent period forachieving the desired delay and throughput performance, and may send thedesired value in the SILENT_AMOUNT_CHANGE-REQ (value) message. Thegreater the silent period, (denoted as Ts), the better the sensingperformance, and on the other hand, the less the time for the trafficdelivery. This may degrade the network performance. However, if thesilent period is too short, the sensing performance may be poor, makingthe DSM system unable to find good channels to operate on and hence mayresult in poor network performance. Accordingly, a proper value may beselected for the silent period. However, similar to the case of PUdetection, there may be a problem with the first approach, because therelationship between silent period and the network performance may beaffected by the protocol behavior and the traffic condition, and it maybe difficult to be accurately captured.

FIG. 18 is an example call flow 1800 of a signal exchange between a MACQoS entity 1805 and a SPME 1810 for SU detection. The call flow may beapplicable to a second approach where probing may be used with a changein an absolute amount. The MAC QoS module 1805 may monitor networkperformance and determine the desired value for Ts for achieving desireddelay and throughput performance (1820) and may send aSILENT_AMOUNT_CHANGE_REQ, (i.e., an increase or decrease), to the SPME1810 (1825). The SPME 1810 may increase/decrease the silent period by acertain amount of time, for example, n ms. For example, Ts←Ts−n orTs←Ts+n. The SPME 1810 may send a SILENT_AMOUNT_CHANGE_RESP message toconfirm whether the requested increase or decrease has occurred (1830).The MAC QoS entity 1805 and SPME 1810 may repeat these messages (1835)until the desired delay and throughput values are obtained (1840).

The example call 1800 may also be applicable for a third approach thatmay use probing and a change in a relative amount. The MAC QoS module1805 may monitor network performance and determine the desired value forTs for achieving desired delay and throughput performance (1820) and maysend a SILENT_AMOUNT_CHANGE_REQ, (i.e., an increase or decrease), to theSPME 1810 (1825). The SPME 1810 may increase/decrease the silent periodby a certain fraction, for example, Ts←Ts(1+v)/Ts←Ts(1−v), where v maybe the fraction of the increase/decrease. The SPME 1810 may send aSILENT_AMOUNT_CHANGE_RESP message to confirm whether the requestedincrease or decrease has occurred (1830). The MAC QoS entity 1805 andSPME 1810 may repeat these messages (1835) until the desired delay andthroughput values are obtained (1840).

The MLME may be modified to support silent period coordination. Periodicsilent periods may be coordinated across the DSM system by transmittingthe silent period information within the beacon. The IEEE 802.11 beaconmay contain a ‘quiet element’ field that defines an interval of timeduring which no transmission should occur in the current channel. This‘quiet element’ may be added to the aggregated beacon and used tocoordinate the silent periods. The quiet element may be modified toaccount for the factors described herein below.

To support the silent period scheduling, the aggregated beacon may sendquiet elements on each of the channels to be aggregated. These quietelements may represent the silent period duration and timing associatedwith all channels. This may ensure the maximum robustness for thesystem, so that if the beacon on one of the four channels is missed, thestation may still be aware of the silent period for all channels basedon the silent period information received on other channels.

FIG. 19 is a diagram of an example quiet element format 1900 for theaggregated channels. The quiet element may have an element ID field 1905of 1 octet, a Length field 1910 of 1 octet, a Quiet Count field 1915 of1 octet, a Quiet Period field 1920 of 1 octet, a Quiet Duration 1925field of 2 octets, a Quiet offset field 1930 of 2 octets, a Ch ID 1field 1935 of 1 octet . . . a CH ID N field of 1 octet.

A single quiet element 1900 may describe the silent period for more thanone channel for the case of channel-synchronous silent periods. Inaddition, a single channel may require multiple quiet elements todescribe the silent periods on it, as shown in the scheduling examples.For a channel with no silent periods defined for it, the quiet durationfield 1925 may be set to 0, or a quiet element 1900 may not be sent onthat channel. This may allow sending of a quiet element 1900 with theQuiet Count field 1930 of 0, which may not be allowed in IEEE 802.11,but may be necessary to ensure stations that first hear the beacon willnot transmit if the current beacon interval contains a silent period.

In addition to this, the Quiet Offset field 1930 may be redefined tosupport silent period intervals, (time between silent periods), of lessthan 100 ms. A Quiet Offset field 1930 having a value of 0 may representa silent period that occurs at most once every beacon period, (assuminga Quiet Period field 1920 having a value of 1). Therefore, setting theQuiet Offset field 1930 to a value of 0 may result in silent periodintervals that are multiples of the beacon period, assuming 100 ms. Whenthe Quiet Offset field 1930 has a value set to a non-zero value, thisvalue may represent the length of time, (in time units (TUs)), betweensilent periods that may occur within the same beacon interval, asopposed to the offset from the start of the target beacon transmissiontime (TBTT) as in IEEE 802.11.

The quiet element 1900 may be modified to keep backward compatibilitywith the IEEE 802.11 quiet element. The length field 1910 may be used toindicate the number of channel identities (ID)s 1935 that may beattached to the end of the quiet element 1900. Each channel ID 1935 mayrepresent one of the channels that may have the periodic silent perioddescribed by this quiet element 1900. In addition, the changes describedherein below may be made to the interpretation of each field. The QuietCount field 1915 may take on a value of zero to indicate that the silentperiod or periods may be within the current beacon interval. When atleast one silent period may occur within each beacon interval, the QuietCount field 1915 may have a value of zero. The Quiet Period field 1920may continue to indicate the value of the number of beacon intervalsbetween quiet periods. In addition, when the Quiet Period field 1920 mayhave a value of 0, the periodicity for this silent period may be smallerthan one beacon interval, for example, there may be more than one silentperiod in the beacon interval. When the Quiet Period field 1920 may havea value of 1 or larger, the Quiet Offset field 1930 may have the sameinterpretation as in IEEE 802.11. When the Quiet Period field 1920 mayhave a value of 0, the Quiet Offset field 1930 may represent theinterval between the silent periods occurring within the beaconinterval.

Due to the advanced notice provided by the Quiet Count field 1915, theMAC entity buffering scheme may prepare itself for the occurrence of ascheduled silent period. Since a given silent period schedule sent on abeacon may supersede all previously scheduled silent periods, silentperiod configuration may be changed at each beacon interval.

An alternative format to the quiet element 1900 may maintain the samefields as in IEEE 802.11 and split each field (quiet count, quietperiod, and the like) into four subfields, where each subfield mayrepresent one of the four channels.

An additional rule that may be followed by stations to ensure robustsensing during the silent time may be for stations to abstain fromtransmitting over any beacon interval when the station did not receivethe beacon on any of the four channels. Since the silent period may bedefined relative to the beacon, (either immediately following thebeacon, or a specified number of TUs following a beacon), exactknowledge of the silent period time(s) in a beacon interval may requirecorrect reception of the beacon for that interval. Since the silentperiod information for all channels may be transmitted on the aggregatedbeacon of each channel, the probability of a station having to abstainfrom transmission during a beacon interval may be low and the loss ofefficiency may be low.

For the case where the number of aggregated channels is low and a highprobability of missing a beacon is expected, the station may be allowedto transmit in the beacon interval where the beacon is missed and thenrely on the silent period information from the previously receivedbeacons. A safe padding may be added to the expected silent period timeto account for the potential of the beacon having been delayed due toretransmissions and CSMA contention delay. This safe padding may bereduced to a reasonable amount by having the beacon referenced to theend of the TBTT.

FIGS. 20A, 20B and 20C are examples of silent period intervals 2000relative to beacon intervals 2005. The examples use the Quiet Offsetfield to configure a silent period having different ranges of silentintervals relative to the beacon interval. In FIG. 20A, the silentperiod interval is greater than the beacon interval. In FIG. 20B, thesilent period interval may be equal to the beacon interval. In FIG. 20C,the silent period interval may be less than the beacon interval.

To simplify the insertion of the silent period within the regular IEEE802.11 operation, the following rules may be used by the MLME. Theserules may be independent of the channel in the aggregation scheme.

The timing of a first silent period 2100 of a beacon interval 2105 withrespect to broadcast and poll messages is shown in FIG. 21. If a silentperiod 2100 is scheduled immediately following the beacon 2110, it mayoccur between the beacon transmission and the traffic indication map(TIM) or delivery traffic indication message (DTIM) interval 2115 wherethe AP may transmit buffered broadcast/multicast frames, or the stationmay poll for buffered unicast frames. This means that stations maywakeup to send the poll message in response to the TIM in the beaconafter the end of the scheduled silent period. This rule may ensure thatthe silent period occurs at a specific period in time, (due to the lackof any contention for frames or acknowledgements (ACKs)), and that theTIM/DTIM interval may remain at a fixed time instant, (since the silentperiod is a fixed number of TUs). Since all stations may be quiet duringthe beacon, the system may know that the silent period may start oncethe beacon has been transmitted by the AP. This knowledge may be used toensure synchronization with the sensing processor/toolbox.

FIG. 22 is a diagram of an example station transmission pattern 2200 atthe arrival of an intra-beacon silent period 2205. For silent periodsthat occur between TBTTs, for example, when the Quiet Offset field isnon-zero, an AP or a station may ensure that its frame transmission maycomplete at least a short interframe space (SIFS) 2210 before thescheduled start of the silent period. This may ensure that the start ofthe silent period coincides with a situation where no transmission iscurrently on the air. The start of a sensing operation may besynchronized with the scheduled start of a silent period.

FIG. 23 is a diagram of an example channel independent silent periodthat may affect non-primary channels. The MLME may allow silent periods2300 on a subset of channels while maintaining the primary channeloperation on the remaining channels. In order to do so, unacknowledgedframes due to the silent period may be retransmitted on the availablechannels.

FIG. 24 is a diagram of an example channel independent silent period2400 that may affect a primary channel. In this example, a primarychannel switch mechanism 2410 may be required. This mechanism may beimplemented by a switch message 2410 sent along with the beacon, asshown in FIG. 24. Other methods of performing the primary channelswitch, such as a scheduled switch configured at each known switch timeusing a separate management message, may also be possible.

Asynchronous Silent Periods may be coordinated with stations using aspecial control channel message containing one or more quiet elements.The control channel message may transmit the quiet elements associatedwith each channel on all channels, for example, the message may berepeated on each of the channels. In the case of an asynchronous silentperiod, only the duration field may be used. The other elements may be“don't care” values. In addition to sending the asynchronous silentperiod message on all channels, the following procedure may be used tofurther improve robustness of the asynchronous silent period to thepossibility of stations not receiving the control message.

FIG. 25 shows an example call flow 2500 for asynchronous silent periodsbetween an AP 2505, STAs 2510, and a sensing processor 2515. The AP may2505 may broadcast the asynchronous silent period control message to allSTAs 2510 stations (2520). Following transmission of the message, the AP2505 may listen to the medium for distributed coordination function(DCF) interframe space (DIFS) (2525). If the medium is quiet for thattime, the AP 2505 may trigger the sensing processor 2515 to initiate thesensing operation with the remaining time specified (2530). If a channelaccess was sensed on the medium by a device belonging to the DSM system,the AP may repeat the first two steps (2535) prior to sending the silentperiod start indication to the sensing processor 2515. The first twosteps may be repeated multiple times up to a predetermined maximumnumber of times. If the medium is still busy after that point, the AP2505 may cancel scheduling of the asynchronous silent period and rely onperiodic silent periods to satisfy the request from the sensingprocessor 2515.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art may appreciate that eachfeature or element may be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, UE, terminal, base station, RNC, or any host computer.

What is claimed is:
 1. A wireless transmit and receive unit (WTRU)comprising: a processor configured to: receive a beacon on a channel,the beacon comprising a quiet element that indicates a silence periodschedule associated with the channel relative to a beacon period,wherein a silence period associated with the channel comprises ano-transmission time period on the channel; determine a silent periodinterval based on a silent period indication and a silent period offsetindication comprised in the quiet element, wherein on a condition thatthe determined silent period interval is smaller than a beacon interval,the quiet element is configured to indicate a length of time between twoadjacent silent periods; determine a start time of the silent periodbased on the determined silent period interval, and a quiet countindication and the silent period offset indication comprised in thequiet element; and refrain from transmitting on the channel during thesilence period.
 2. The WTRU of claim 1, wherein on a condition that thedetermined silent period interval is greater than a beacon interval, thesilent period offset indication indicates a length of time between thebeacon and the silent period.
 3. The WTRU of claim 1, wherein the silentperiod offset indication indicates the length of time between twoadjacent silent periods associated with the channel within one beaconinterval.
 4. The WTRU of claim 1, wherein the silent period indicationindicates a periodicity of the silent period relative to a beaconinterval.
 5. The WTRU of claim 4, wherein the silent period indicationhaving a value of zero indicates that the silent period interval issmaller than the beacon interval.
 6. The WTRU of claim 4, wherein thesilent period indication having a non-zero value indicates a number ofbeacon intervals in a silent period interval.
 7. The WTRU of claim 1,wherein the processor is further configured to: determine a silentperiod duration associated with the channel based on a silent periodduration indication comprised in the quiet element, wherein the sensingis performed for the determined silent period duration.
 8. The WTRU ofclaim 1, wherein the silent period offset indication indicates a numberof time units between two adjacent silent periods associated with thechannel within one beacon interval.
 9. The WTRU of claim 1, wherein thequiet count indication having a value of zero indicates that the silenceperiod occurs in a current beacon interval.
 10. The WTRU of claim 1,wherein the beacon comprises an aggregated beacon for an aggregatedchannel set that comprises the channel, and the quiet element indicatesa plurality of silent periods associated with a plurality of channels inthe aggregated channel set.
 11. A method comprising: receiving a beaconon a channel, the beacon comprising a quiet element that indicates asilence period associated with the channel relative to a beacon period,the silence period comprises a no-transmission time period on thechannel; determining a silent period interval based on a silent periodindication and a silent period offset indication comprised in the quietelement; determining a start time of the silent period based on thedetermined silent period interval, and a quiet count indication and thesilent period offset indication comprised in the quiet element, whereinon a condition that the determined silent period interval is smallerthan a beacon interval, the quiet element is configured to indicate alength of time between two adjacent silent periods; and refraining fromtransmitting on the channel during the silence period.
 12. The method ofclaim 11, wherein on a condition that the determined silent periodinterval is greater than a beacon interval, the silent period offsetindication indicates a length of time between the beacon and the silentperiod.
 13. The method of claim 11, wherein the silent period offsetindication indicates the length of time between two adjacent silentperiods associated with the channel within a beacon interval.
 14. Themethod of claim 11, wherein the silent period indication indicates aperiodicity of the silent period relative to a beacon interval.
 15. Themethod of claim 14, wherein the silent period indication having a valueof zero indicates that periodicity of the silent period is smaller thanthe beacon interval.
 16. The method of claim 14, wherein the silentperiod indication having a non-zero value indicates a number of beaconintervals in a silent period interval.
 17. The method of claim 11,further comprising: determining a silent period duration associated withthe channel based on a silent period duration indication comprised inthe quiet element, wherein the sensing is performed for the determinedsilent period duration.
 18. The method of claim 11, wherein the silentperiod offset indication indicates a number of time units between twoadjacent silent periods associated with the channel within one beaconinterval.
 19. The method of claim 11, wherein the quiet count indicationhaving a value of zero indicates that the silence period occurs in acurrent beacon interval.
 20. The method of claim 11, wherein the beaconcomprises an aggregated beacon for an aggregated channel set thatcomprises the channel, and the quiet element indicates a plurality ofsilent periods associated with a plurality of channels in the aggregatedchannel set.